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International audience; The estimation of sand fluxes in large rivers is an important issue because of its significant role on the river morphodynamic. However, these fluxes are very difficult to measure and compute because of their large spatial and temporal variability. Equations can be used to compute the sediment transport capacity but the actual sediment transport may be lower than this capacity when sand supply is limited, especially for gravel bed rivers like the Rhône River, France. This study presents the results of a comparison between recent flux measurement surveys on the Rhône River in Lyon and a simple physically based model for computing the sand transport capacity. Flux measurements were achieved combining ADCP measurements and direct sampling using a Niskin sampler. Seven field surveys were carried out, most of them during a 10-year flood in 2018. The range of investigated discharges varies from 900 m3/s to 2700 m3/s during different phases of the flood. Each experiment is made of a set of 12 samples distributed on a cross section, velocities and bathymetry being acquired with an ADCP. The analyses were carried out by sieving and filtering. On the other hand, sediment transport is estimated using a semi-empirical sediment transport formula for suspended load. The model is based on stage-discharge relationships to estimate the main hydraulic parameters, such as the bed shear stress. This model was implemented on two cross-sections with relatively different hydrodynamic conditions, and results were compared with measurements. It is interesting to observe that the transport capacity is reached for the less dynamic cross-section, which appears to control sand transport over the whole reach.We established a suspended sand rating curve for this cross section and experimental results were correctly predicted by the model. However, uncertainties need to be evaluated before establishing reliable sand fluxes time series and budgets.

River Flow 2018: 9th International Conference on Fluvial Hydraulics, Lyon, FRA, 05-/09/2018 - 08/09/2018; International audience; SSC (Suspended Solid Concentration) measurements in rivers are a complex scientific issue. Many questions arise on the spatial and temporal distribution of particles throughout a cross-section, on the properties of particles and grain-size, and also on the sediment transport capacity of streams and rivers. In this study, we focused on the SSC and grain size distribution measured from river samples, automatically or manually acquired. Many agencies suggested slightly different methods for measuring SSC: The European standard NF EN 872, which related to the US EPA 160.2 requires sub-sampling using shake-and-pour aliquot selection. The APHA 2540D requires sub-sampling by pipetting at mid-depth in the original sample shaken with a magnetic stirrer. These methods lead to significant uncertainty when particles larger than 63 µm are present in the samples. The ASTM D3977 analysis method, endorsed by the USGS is more accurate to capture and quantify particles larger than 63 µm. In this study we confirm the sub-sampling problem in a large concentration range using a set of samples from an alpine river.

River Flow 2018: 9th International Conference on Fluvial Hydraulics, Lyon, FRA, 05-/09/2018 - 08/09/2018; International audience; In this paper, we present some first attempt to measure graded sus-pension of sands in an alpine river. It is a real challenge to measure graded-suspensions of sands in such dynamic rivers. Specific measurements of the graded suspension in the middle of a secondary channel were attempted using a sampler that allows simultaneous sampling at three different elevations (5 cm, 10 cm, and 20 cm) above the bed. Very large concentrations (up to C = 40 g/l) of fine sediments in suspension were measured during a dam reservoir flush-ing event. It included large amounts of sand (from 10 to 60% of the measured concentration). A substantial graded suspension of sand was measured even for relatively low velocities. Sand fluxes estimates for varying bed shear stresses during the event are discussed. In particular, based on the measured bed shear stress, a semi-empirical formula developed for sand suspension is applied to test its ability to predict sand flux in alpine rivers. The sensibility of such formula to the grain size is very high whereas large uncertainties exist in the measure-ment (d50 varies from 0.1 to 0.3 mm depending on the sample), which makes its application difficult at the moment.

L'Observatoire des Sédiments du Rhône (OSR), mis en place en 2009, vise à améliorer les connaissances scientifiques sur les dynamiques sédimentaires du fleuve et des contaminants associés. Les programmes précédents (OSR 2 et OSR 3), ont permis d'acquérir des informations plus précises sur la présence et les concentrations de contaminants prioritaires dans les matières en suspension du Rhône et de ses principaux affluents. Ce rapport vise à interpréter les données acquises par l'OSR sur les principales stations du réseau de suivi, en les complétant au préalable pour des substances non ou peu documentées, dans le but de formuler des recommandations à destination de l'AERMC concernant les substances à inclure dans un futur réseau de mesure des flux particulaires pérenne sur le bassin du Rhône. Pour ce faire, une démarche de priorisation et de sélection des substances pertinentes a été mise en oeuvre, à partir de critères tels que la présence dans les textes réglementaires, l'affinité pour les particules, la fréquence de quantification, la toxicité, etc. Au total, 298 substances ont été évaluées. Suite à cette démarche de priorisation, l'ensemble des données acquises sur les concentrations en contaminants des matières en suspension ont été regroupées et interprétées, afin d'établir un état des lieux détaillé des polluants prioritaires et émergents sur le bassin du Rhône en termes de tendances spatio-temporelles et de risque environnemental. L'influence des conditions hydrologiques et des saisons est également abordée. En parallèle, des analyses prospectives de méthylmercure, composés pharmaceutiques et hormones ont été menées sur des échantillons de matières en suspension prélevées sur le Rhône et plusieurs de ses affluents. Les résultats montrent que le Gier et la Bourbre sont les affluents sur lesquels les concentrations en ces contaminants émergents sont les plus élevées. En revanche, à Jons et Arles sur le Rhône, ces substances sont moins fréquemment quantifiées.

Ce livrable correspond à l'action III.3 de l'Observatoire des Sédiments du Rhône, programme 2015-2017 (OSR 4). Il a pour objet la quantification des flux de matières en suspension et des contaminants associés, du Lac Léman à la mer Méditerranée. Les chroniques de concentration en micropolluants (PCB indicateurs, mercure, éléments traces métalliques et radionucléides), de débit et de matières en suspension (MES) acquises par l'OSR et ses partenaires depuis sa mise en place sont bancarisées dans la Base de Données des Observatoires en Hydrologie (BDOH), qui permet également le calcul automatisé de flux de MES et de contaminants associés. Dans une première partie, le fonctionnement de cette base est décrit. Une méthodologie spécifique et harmonisée a été développée pour combler les lacunes temporelles des chroniques bancarisées. Elle est détaillée dans une deuxième partie. Puis les flux de matières en suspension sont calculés pour la période 2011-2016 via cette méthodologie spécifique et interprétés dans une troisième partie. Enfin, les flux de contaminants sont actualisés et interprétés en termes de bilans annuels à l'échelle du bassin du Rhône pour les années 2014, 2015 et 2016.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU [ADD1_IRSTEA]Hydrosystèmes et risques naturels [ADD2_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; Ce livrable correspond à l'action III.3 de l'Observatoire des Sédiments du Rhône, programme 2015-2017 (OSR 4). Il a pour objet la quantification des flux de matières en suspension et des contaminants associés, du Lac Léman à la mer Méditerranée. Les chroniques de concentration en micropolluants (PCB indicateurs, mercure, éléments traces métalliques et radionucléides), de débit et de matières en suspension (MES) acquises par l'OSR et ses partenaires depuis sa mise en place sont bancarisées dans la Base de Données des Observatoires en Hydrologie (BDOH), qui permet également le calcul automatisé de flux de MES et de contaminants associés. Dans une première partie, le fonctionnement de cette base est décrit. Une méthodologie spécifique et harmonisée a été développée pour combler les lacunes temporelles des chroniques bancarisées. Elle est détaillée dans une deuxième partie. Puis les flux de matières en suspension sont calculés pour la période 2011-2016 via cette méthodologie spécifique et interprétés dans une troisième partie. Enfin, les flux de contaminants sont actualisés et interprétés en termes de bilans annuels à l'échelle du bassin du Rhône pour les années 2014, 2015 et 2016.

International audience; Mediterranean regions are prone to intense rainfall events that can lead to devastating flash floods, sometimes associated with high sediment transport. They generally occur in small catchments (less than 20 km2) that are generally ungauged. During these events, rainfall is also very variable both in time and in space and high resolution rainfall fields are necessary to understand the corresponding hydro-sedimentary response. We present a dedicated observation strategy set up in the 116 km2, Auzon catchment (Ardèche, France, OHMCV observatory) that led to the collection of a high space time resolution of rainfall, discharge and suspended sediment data set (Nord et al., ESSD, 2017). Rainfall field estimates combine rain gauges and radar data. Flooding discharges are obtained using standard discharge gauging stations and non-contact measurements: opportunistic flood gaugings using Surface Velocimetry Radar (SVR), LS-PIV (Large scale particle image velocimetry) in fixed stations or based on videos from You Tube. Discharge and suspended sediment are monitored on nested scales ranging from the plot scale to the medium-size catchment scale, allowing relating observed fluxes and diffuse sources of sediments. All these data sets provide information about flash floods space-time characteristics and associated processes that are of interest for a better management of this kind of events and for understanding associated human behavior and damages to properties. Monitoring of suspended sediments is also necessary to study the transport of nutriments and contaminants.

HMEM, Durham, New Hampshire, USA, 09-/07/2017 - 12/07/2017; International audience; Stage-discharge rating curves are used to relate streamflow discharge to continuously measured river stage readings to create a continuous record of streamflow discharge. The stage-discharge relationship is estimated and refined using discrete streamflow measurements over time, during which both the discharge and stage are measured. There is uncertainty in the resulting rating curve due to multiple factors including the curve-fitting process, assumptions on the form of the model used, fluvial geomorphology of natural channels, and the approaches used to extrapolate the rating equation beyond available observations. This rating curve uncertainty leads to uncertainty in the streamflow timeseries, and therefore to uncertainty in predictive models that use the streamflow data. Many different methods have been proposed in the literature for estimating rating curve uncertainty, differing in mathematical rigor, in the assumptions made about the component errors, and in the information required to implement the method at any given site. This study describes the results of an international experiment to test and compare streamflow uncertainty estimation methods from 7 research groups across 9 institutions. The methods range from simple LOWESS fits to more complicated Bayesian methods that consider hydraulic principles directly. We evaluate these different methods when applied to three diverse gauging stations using standardized information (channel characteristics, hydrographs, and streamflow measurements). Our results quantify the resultant spread of the stage-discharge Quantifying the uncertainty of discharge measurements (or "gaugings") is a challenge in the hydrometric community. A useful tool to empirically estimate the uncertainty of a gauging method is the field inter-laboratory experiment (Le Coz et al., 2016). Previous inter-laboratory experiments conducted in France (in 2009, 2010, 2011 and 2012) showed that the expanded uncertainty (with a probability level of 95%) of an ADCP gauging made of six successive transects is typically around 5% under optimum site conditions (straight reach, uniform and smooth streambed cross-section, homogeneous flow, etc.) and may be twice higher under poorer site conditions. In practice, the selected cross-section does not always match all quality requirements which may result in larger uncertainty. However, the uncertainty due to site selection is very difficult to estimate with predictive equations. From 9 to 10 November 2016, 50 teams from 8 different countries, using 50 ADCPs simultaneously, conducted more than 600 discharge measurements in steady flow conditions (~14 m3/s released by a dam). 26 cross-sections with various shapes and flow conditions were distributed over 500 meters along the Taurion River at Saint-Priest-de-Taurion, France. A specific experiment protocol, which consisted of circulating every team over half of the cross-sections, was implemented in order to quantify the impact of site selection on the discharge measurement uncertainty. Beyond the description of the experiments, uncertainty estimates are presented. The overall expanded uncertainty of a 6-transect ADCP gaugings (duration around 720 seconds) is estimated to be around 6%.The uncertainty of the discharge measurements varies among the cross-sections. These variations are well correlated to the expert judgment on the cross-section quality made by each team. First results seem to highlight a relation between uncertainty computed for each cross-section and criteria such as flow shallowness and measured discharge ratio. Further investigations are necessary to identify the criteria related to error sources that are possibly meaningful for categorizing measurement conditions and site selection. Moreover, experimental uncertainty and the uncertainty predicted by analytical methods such as QRev, QUant, OURSIN, RiverFlowUA or QMSys software will be compared.

International audience; By combining noncontact streamgauging methods (LSPIV, radar) and the BaRatin method, we were able to build quickly a rating curve on a large flow range for an intermittent stream.; En combinant des jaugeages sans contact (LSPIV, radar) et la méthode BaRatin nous avons pu construire rapidement une courbe de tarage pour une gamme de débit étendue sur un petit cours d’eau intermittent.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUThe contract of Simon Gérard was funded by the Institut National des Sciences de l’Univers (INSU/CNRS).; International audience; A comprehensive hydrometeorological dataset is presented spanning the period 1 January 2011-31 December 2014 to improve the understanding of the hydrological processes leading to flash floods and the relation between rainfall, runoff, erosion and sediment transport in a mesoscale catchment (Auzon, 116 km 2) of the Mediterranean region. Badlands are present in the Auzon catchment and well connected to high-gradient channels of bedrock rivers which promotes the transfer of suspended solids downstream. The number of observed variables, the various sensors involved (both in situ and remote) and the space-time resolution (∼ km 2 , ∼ min) of this comprehensive dataset make it a unique contribution to research communities focused on hydrom-eteorology, surface hydrology and erosion. Given that rainfall is highly variable in space and time in this region, the observation system enables assessment of the hydrological response to rainfall fields. Indeed, (i) rainfall data are provided by rain gauges (both a research network of 21 rain gauges with a 5 min time step and an operational network of 10 rain gauges with a 5 min or 1 h time step), S-band Doppler dual-polarization radars (1 km 2 , 5 min resolution), disdrometers (16 sensors working at 30 s or 1 min time step) and Micro Rain Radars (5 sensors, 100 m height resolution). Additionally, during the special observation period (SOP-1) of the HyMeX (Hydrolog-ical Cycle in the Mediterranean Experiment) project, two X-band radars provided precipitation measurements at Published by Copernicus Publications. 222 G. Nord et al.: High-resolution hydrometeorological data in a mesoscale Mediterranean catchment very fine spatial and temporal scales (1 ha, 5 min). (ii) Other meteorological data are taken from the operational surface weather observation stations of Météo-France (including 2 m air temperature, atmospheric pressure, 2 m relative humidity, 10 m wind speed and direction, global radiation) at the hourly time resolution (six stations in the region of interest). (iii) The monitoring of surface hydrology and suspended sediment is multi-scale and based on nested catchments. Three hydrometric stations estimate water discharge at a 2-10 min time resolution. Two of these stations also measure additional physico-chemical variables (turbidity, temperature, conductivity) and water samples are collected automatically during floods, allowing further geochemical characterization of water and suspended solids. Two experimental plots monitor overland flow and erosion at 1 min time resolution on a hillslope with vineyard. A network of 11 sensors installed in the intermittent hydrographic network continuously measures water level and water temperature in headwater subcatchments (from 0.17 to 116 km 2) at a time resolution of 2-5 min. A network of soil moisture sensors enables the continuous measurement of soil vol-umetric water content at 20 min time resolution at 9 sites. Additionally, concomitant observations (soil moisture measurements and stream gauging) were performed during floods between 2012 and 2014. Finally, this dataset is considered appropriate for understanding the rainfall variability in time and space at fine scales, improving areal rainfall estimations and progressing in distributed hydrological and erosion modelling.

In recent years, stage / velocity radar stations have been installed in France. This type of stations provides measurements of water level and surface velocity at a fixed point of the cross-section. Discharge is calculated as the product of the wetted area and cross-sectional average velocity; respectively obtained using a stage-area scale S(h) established from a bathymetry profile, and a relation between the index velocity measured by the radar (Vi) and the cross-sectional average velocity (Vmean), established with gaugings. This is the «index velocity method ».As discussed through various examples, the index velocity method has advantages over traditional stage-discharge rating curves: - Flood extrapolations are better known: velocity varies more slowly than water discharge with stage and the stage-area relation can be predicted. - Managing bed evolution is easier because the Vmean(Vi) relation changes little and the S(h) relation is easy to reset with a bathymetry survey. - Monitoring the Vi (h) measured relation in real time allows detecting rating changes of the station. The wider use of the method and the development of measurement instruments will allow the future assessment of the uncertainty related to the calculation of water discharge. Perspectives for the bayesian analysis of index velocity ratings are discussed. / Depuis quelques années, des stations radar hauteur-vitesse ont été mises en service en France. Ce type de station fournit une mesure de hauteur d'eau et de vitesse de surface en un point fixe de la section. Le débit est calculé comme le produit de la surface mouillée et de la vitesse débitante. La surface mouillée est obtenue via une relation hauteur-surface S(h) établie à partir d'un profil bathymétrique ; et la vitesse débitante est calculée via une relation entre la vitesse mesurée par radar (Vi) et la vitesse moyenne dans la section (Vmoy), établie à partir de jaugeages. Il s'agit de la «méthode de la vitesse témoin» ou «index velocity method». Comme nous le verrons au travers d'exemples sur différentes stations, la méthode présente des avantages par rapport aux courbes de tarage hauteur-débit : - les extrapolations en crue sont mieux documentées, la vitesse évoluant plus faiblement que le débit avec la hauteur et la relation hauteur-surface étant connue par ailleurs. - la gestion des détarages est plus facile car la relation Vmoy(Vi) évolue peu et la relation S(h) est facile à recaler avec un seul levé bathymétrique. - l'évolution de la relation Vi(h), mesurée en temps réel, permet de détecter les anomalies, signes de détarages potentiels de la station. L'utilisation plus large de la méthode et le développement des instruments de mesure permettra à l'avenir de mieux évaluer l'incertitude liée au calcul du débit. Des perspectives pour l'analyse bayésienne des stations vitesse témoin sont discutées.

Ce document a la double vocation de servir de guide pratique, synthétique et accessible à l'ensemble des hydromètres, mais aussi d'ouvrage de référence sur l'état de l'art de l'hydrométrie. Cette nouvelle édition expose les défis auxquels les services d'hydrométrie doivent répondre, met en avant de nouvelles techniques de mesures (non intrusives notamment), insiste sur l'importance de mieux connaître et diffuser les incertitudes associées aux données et rappelle les règles essentielles de prévention pour la sécurité des hydromètres.

Quantifying the uncertainty of discharge measurements (or “gaugings”) is a challenge in the hydrometric community. A useful tool to empirically estimate the uncertainty of a gauging method is the field inter-laboratory experiment (Le Coz et al., 2016). Previous inter-laboratory experiments conducted in France (in 2009, 2010 and 2012) showed that the expanded uncertainty of an ADCP gauging (considering an average discharge over six successive transects) is typically around 5% (with a probability level of 95%), under optimum measurement conditions (straight reach, uniform and smooth streambed cross-section, homogeneous flow, etc.). In practice, the selected cross-section does not always match all quality requirements which may result in larger uncertainty. However, the uncertainty due to site selection is very difficult to estimate with predictive equations. From 8 to 10 November 2016, 50 laboratories or teams (from 8 different countries) with 50 ADCPs, simultaneously conducted more than 600 ADCP discharge measurements in steady flow conditions (around 14 m3=s released by a dam), during three half-days, over 500 m along the Taurion River at Saint-Priest-de-Taurion, France. 26 cross-sections with various shapes and flow conditions, and more or less favourable conditions, were distributed along the river. A specific experiment procedure, which consisted of circulating every team over half of the cross-sections, was implemented in order to quantify the impact of site selection on the discharge measurement uncertainty. Beyond the description of the experiments, uncertainty estimates are presented. The overall expanded uncertainty is estimated to be around 6% at 95% level of confidence for a measurement performed with 6 transects in the given measurement conditions of the experiments. However, the uncertainty of the discharge measurements varies among the cross-sections. These variations are well correlated to the expert judgment on the cross-section quality made by each team. First results seems to highlight a relation between uncertainty computed for each cross-section and criteria such as the shallowness of the flow, the unmeasured discharge ratio. Further investigations are necessary to identify the criteria related to error sources that are possibly meaningful for categorizing measurement conditions and site selection. Moreover, comparison between experimental uncertainty and analytical methods (such as computations recently proposed by QRev, Quant, Oursin or QMSys software) is planned to be done.; Du 8 au 10 novembre 2016, le Groupe Doppler Hydrométrie a organisé sur le Taurion, à l’aval du barrage-usine de Chauvan, une campagne d’essais interlaboratoires de mesures de débit par profileur hydro-acoustique ADCP. En plus de permettre aux équipes participantes de confronter leurs outils et leurs pratiques, les essais interlaboratoires visent à contribuer collectivement à l’amélioration de la maîtrise de ces mesures et de leurs incertitudes. En l’absence de mesure de référence en termes de débit, les intercomparaisons constituent en effet un moyen utile pour quantifier l’incertitude de la technique de mesure dans des conditions de mesure données (Blanquart, 2013; Dramais et al., 2013; Le Coz et al., 2016). Cette 5ème campagne interlaboratoire du Groupe Doppler Hydrométrie (après celles de la Vézère en 2009, de Génissiat en 2010 et 2012 ainsi que celle du canal de la Gentille en 2011) a rassemblé 50 participants (ou équipes de mesure) français et étrangers issus d’organismes publics ou privés, permettant la réalisation de plus de 600 mesures de débit réparties sur 3 demi-journées en profitant de débits stables délivrés par le barrage-usine de Chauvan, de l’ordre de 14 m3=s. Les essais interlaboratoires de Chauvan se distinguent par leur dimension et par l’originalité du protocole d’essai mis en oeuvre. Alors que les campagnes précédentes ont eu lieu sur des sites de mesure plutôt favorables, caractérisés par des géométries de section en travers relativement simples, des sections de mesure plus variées et complexes ont cette fois été choisies (faibles profondeurs, écoulements parfois perturbés par des obstacles). Ainsi des permutations ont été réalisées par 48 participants parmi les 24 sections de mesure présentant des conditions de déploiement plus ou moins favorables pour les ADCP. En parallèle, le débit a été mesuré en continu par deux ADCP (StreamPro et Q-Liner) sur des sections de mesure fixes et les hauteurs d’eau ont été enregistrées par trois capteurs limnimétriques (deux sondes piézométriques relatives (Paratronic) disposées sur deux sections de mesure et un radar (VEGA) au niveau de la station hydrométrique EDF-DTG). Le suivi limnimétrique a permis de confirmer la stabilité du débit du cours d’eau (variations inférieures à 1 cm) au cours des trois sessions de mesure. Les résultats de débit des ADCP sont peu dispersés (écarts-types de l’ordre de 0,400 m3=s) et la valeur de débit moyenne (référence construite) est proche des valeurs fournies par les mesures indépendantes à moins de 5% près (jaugeages par ADCP en continu aux deux sections fixes, jaugeage par la méthode globale de dilution et débit associé à la courbe de tarage selon la méthode de tracé conventionnelle, selon la méthode GesDyn ou selon la méthode BaRatin). Les premiers résultats montrent que la dispersion des valeurs de débit semble nettement corrélée à la qualité des sections de mesure évaluée in situ par les équipes de mesure ainsi qu’au ratio du débit mesuré. Les essais interlaboratoires conduisent à une évaluation d’incertitude de l’ordre de 6% (au niveau de confiance de 95 %, soit un facteur d’élargissement k=2) pour un jaugeage par ADCP comportant 6 transects de mesure (dans les conditions de l’essai). Le nombre important de participants rassemblés permet une évaluation précise de cette incertitude de mesure bien que l’estimation de l’incertitude liée au biais de la technique de mesure reste problématique. Cette estimation reste néanmoins à affiner après homogénéisation des traitements des mesures à l’aide du logiciel QRev (Mueller, 2016). La permutation des équipes au sein des différentes sections de mesure permettra la conduite d’une étude statistique visant à isoler l’incertitude liée à la section de mesure. Les résultats préliminaires tendent à montrer l’utilité de mesurer le débit sur plusieurs sections de mesure afin de réduire l’incertitude sur l’estimation du débit. Enfin nous prévoyons de comparer les estimations d’incertitude par propagation des incertitudes telles que proposées par les logiciels Oursin (CNR), QRev (USGS), RiverFlowUA (South Florida Water management District), QMSys ou encore QUANT (Water Survey of Canada) aux résultats d’incertitude issus de ces essais interlaboratoires.

A simple rating curve model using two water level measurements is proposed for tidal rivers. It is based on the Manning-Strickler equation adapted for possible negative slopes resulting from a negative discharge (upstream directed). The model calibration can be achieved thanks to two parameters only: the Strickler coefficient and the temporal lag between the measured slope and the slope to be applied at the reference section. The model has been applied to two tidal rivers for which ADCP gaugings have been achieved during two tidal cycles: the Saigon River in Vietnam and the Seine River in France. Results are encouraging for the Saigon River where water level variations remain mild. For the Seine River case, results are not as good due to a sharp variation of the water level and discharge during the flow tide that makes the calibration difficult. Nevertheless, the proposed model appears to be valid for tidal rivers as soon as the discharge temporal gradient during the tide flow remains moderate.

Ce rapport présente les résultats obtenus suite aux campagnes de mesures de 2015 à 2017. Ils incluent des développements méthodologiques et expérimentaux ainsi que les premiers jeux de données sur les sites pilotes de l'OSR : à Chancy-les-Ripes et Bognes autour de la retenue de Génissiat, à Champagneux, et au niveau de la confluence avec l'Isère pour le secteur nord, et enfin en Arles et au niveau du bac de Barcarin pour le secteur sud. Une discussion est proposée sur l'application de courbes de tarage sédimentaire sur ces différents sites. Enfin, un paragraphe est plus particulièrement proposé sur le développement de la mesure des flux de sables en suspension par une méthode acoustique.

L'action III.1 du programme OSR 4 vise à estimer les flux de matières en suspension (MES) et de contaminants associés sur le Rhône et ses principaux affluents. Pour répondre à cet objectif, un réseau de mesure en continu des concentrations en MES et de prélèvements de MES a été mis en place. Ce document décrit les interventions et les mesures réalisées sur le réseau d'observation des flux particulaires de l'OSR pour l'année 2017 (OSR 4). Il présente également l'avancement de la bancarisation des données issues de ce suivi dans la base de données BDOH/OSR (flux). L'année 2017 a été marquée par la mise en place d'une nouvelle station sédimentaire sur le Gardon à Remoulins. Dans BDOH, les chroniques de concentrations en contaminants comportant des lacunes ont été reconstituées à l'aide de forfaits déterminés par gamme de débits.

Normalization allows to define a common language among the actors in a particular field, to clarify, to harmonize practices and to define the level of quality, safety and less environmental impact of practices. In France, in the field of hydrometry, the normalization work is carried out by the AFNOR / X10C commission. After several years of inactivity, the commission was recently reactivated two years ago, under the impulse of a few motivated actors. The objective of this paper is to highlight the added value of standardization in the hydrometry activity, through a few concrete examples of standards. The organization of standardization at national and international level may seem complex. A presentation of the different standardization structures is therefore proposed, as well as the process of developing a standard.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUFLOODrisk 2016, 3rd European Conference on Flood Risk Management, Innovation, Implementation, Integration, Lyon, FRA, 18-/10/2016 - 20/10/2016; International audience; The Mediterranean area is prone to intense rainfall events triggering flash floods, characterized by very short response times that sometimes lead to dramatic consequences in terms of casualties and damages. These events can affect large territories, but their impact may be very local in catchments that are generally ungauged. These events remain difficult to predict and the processes leading to their generation still need to be clarified. The HyMeX initiative (Hydrological Cycle in the Mediterranean Experiment, 2010-2020) aims at increasing our understanding of the water cycle in the Mediterranean basin, in particular in terms of extreme events. In order to better understand processes leading to flash floods, a four-year experiment (2012-2015) was conducted in the Cévennes region (South-East) France as part of the FloodScale project. Both continuous and opportunistic measurements during floods were conducted in two large catchments (Ardèche and Gard rivers) with nested instrumentation from the hillslopes to catchments of about 1, 10, 100 to 1000 km2 covering contrasted geology and land use. Continuous measurements include distributed rainfall, stream water level, discharge, water temperature and conductivity and soil moisture measurements. Opportunistic measurements include surface soil moisture and geochemistry sampling during events and gauging of floods using non-contact methods: portable radars to measure surface water velocity or image sequence analysis using LS-PIV (Large Scale Particle Image Velocimetry). During the period 2012-2014, and in particular during autumn 2014, several intense events affected the catchments and provided very rich data sets. Data collection was complemented with modelling activity aiming at simulating observed processes. The modelling strategy was setup through a wide range of scales, in order to test hypotheses about physical processes at the smallest scales, and aggregated functioning hypothesis at the largest scales. During the project, a focus was also put on the improvement of rainfall fields characterization both in terms of spatial and temporal variability and in terms of uncertainty quantification. Rainfall reanalyses combining radar and rain gauges were developed. Rainfall simulation using a stochastic generator was also performed. Another effort was dedicated to the improvement of discharge estimation during floods and the quantification of streamflow uncertainties using Bayesian techniques. The paper summarizes the main results gained from the observations and the subsequent modelling activity in terms of flash flood process understanding at the various scales. It concludes on how the new acquired knowledge can be used for prevention and management of flash floods.

FloodRisk 2016, Lyon, FRA, 17-/10/2016 - 21/10/2016; International audience; New communication and digital image technologies have enabled the public to produce and share large quantities of flood observations. Valuable hydraulic data such as water levels, flow rates, inundated areas, etc., can be extracted from photos and movies taken by citizens and help improve the analysis and modelling of flood hazard. We introduce recent citizen science initiatives which have been launched independently by research organisations to document floods in some catchments and urban areas of France, Argentina and New Zealand. Key drivers for success appear to be: a clear and simple procedure, suitable tools for data collecting and processing, an efficient communication plan, the support of local stakeholders, and the public awareness of natural hazards.

International audience; The applicability of a portable, commercially available surface velocity radar (SVR) for noncontact stream gauging was evaluated through a series of field-scale experiments carried out in a variety of sites and deployment conditions. Comparisons with various concurrent techniques showed acceptable agreement with velocity profiles, with larger uncertainties close to the banks. In addition to discharge error sources shared with intrusive velocity-area techniques, SVR discharge estimates are affected by flood-induced changes in the bed profile and by the selection of a depth-averaged to surface velocity ratio, or velocity coefficient (a). Cross-sectional averaged velocity coefficients showed smaller fluctuations and closer agreement with theoretical values than those computed on individual verticals, especially in channels with high relative roughness. Our findings confirm that a 0.85 is a valid default value, with a preferred site-specific calibration to avoid underestimation of discharge in very smooth channels (relative roughness < 0.001) and overestimation in very rough channels (relative roughness>0.05). Theoretically derived and site-calibrated values of a also give accurate SVR-based discharge estimates (within 10%) for low and intermediate roughness flows (relative roughness 0.001 to 0.05). Moreover, discharge uncertainty does not exceed 10% even for a limited number of SVR positions along the cross section (particularly advantageous to gauge unsteady flood flows and very large floods), thereby extending the range of validity of rating curves.

International audience; While the application of uncertainty propagation methods to hydrometry is still challenging, in situ collaborative interlaboratory experiments are a valuable tool for empirically estimating the uncertainty of streamgauging techniques in given measurement conditions. We propose a simple procedure for organizing such experiments and processing the results according to the authoritative ISO standards related to interlaboratory experiments, which are of common practice in many metrological fields. Beyond the computation and interpretation of the results, some issues are discussed as regards: the estimation of the streamgauging technique bias in the absence of accurate enough discharge references in rivers; the uncertainty of the uncertainty estimates, according to the number of participants and repeated measurements; the criteria related to error sources which are possibly meaningful for categorizing measurement conditions. The interest and limitations of the in situ collaborative interlaboratory experiments are exemplified by an application to the hydro-acoustic profiler (ADCP) streamgauging technique conducted in 2010 at two different sites downstream of Génissiat hydropower plant in the Rhône river, France. Typically, the expanded uncertainty (with a probability level of 95%) of the average discharge over 6 successive transects varied from +/-5% at one site with favourable conditions to +/-9% at the other site due to unstable flow conditions.

Observation et modélisation hydro-météorologique multi-échelle pour la compréhension et la simulation des crues éclairs. Quels apports pour les gestionnaires de territoires et les fournisseurs de services?; International audience; Chaque année, spécialement à l’automne, des épisodes pluvieux intenses, dits Méditerranéens, affectent les départements du sud de la France. Ces épisodes, conduisant à des cumuls de pluie importants (quelques centaines de mm en quelques heures ou quelques jours). La figure de la diapo 1, tirée du site de Météo-France ;présente le nombre d’épisodes par an avec un cumul de pluie >150mm /jour et on voit que les départements du sud de la France, principalement le Gard, l’Ardèche et l’Hérault sont les départements les plus affectés. Ces épisodes de pluie conduisent souvent à des crues rapides, parfois dévastatrices. Les exemples récents incluent Nîmes en 1988, Vaison la Romaine en 1992, l’Aude en 1999, le Gard en 2002, le Var en 2010 ou les Alpes Maritimes en 2015, sans oublier la dizaine d’épisodes ayant affecté le sud de la France en 2014. Les conséquences de ces crues sont des submersions de bâtiments, mais aussi des coupures de route sur des petits cours d’eau coupant le réseau hydrographique. L’analyse des victimes de la crue de septembre 2002 dans le Gard a ainsi montré qu’environ la moitié des victimes, plutôt jeunes, avaient péri sur des petits bassins de taille 1000 km (Ruin et al., 2008). Sur les petits bassins, il y a très peu d’informations car, en France, la majorité des stations hydrométriques concernent des bassins de plus de 50 km et l’alerte hydrologique (Vigicrues) concerne les cours d’eau principaux.

International audience; Alpine gravel-bed rivers are characterized by very poorly sorted sediments and significant grain sorting is generally observed on gravel bars. The purpose of this paper is to present some field measurements achieved on the Arc en Maurienne River, France. The main objective is to characterize the dynamics of fine sediments, mainly infiltration, for conditions close to the incipient motion of gravels. The field campaign was carried out on a gravel bar located 10 km downstream of St Jean de Maurienne during the dam flushing event on June 17th, 2014. Patches made of gravels and pebbles were settled on the gravel and infiltration of fine sediment was measured after the event. During the flushing event, surface velocities over the gravel bar were measured thanks to video analysis (LSPIV). Water levels and mean slope in the secondary channel were measured thanks to pressure gauges positioned on the side of the secondary channel. An estimation of the bed shear stresses over the patches was thus possible all along the event. Intense water sampling was also carried out both upstream and downstream the secondary channel. Grain size analysis showed that deposited sediments were much coarser than sediments in suspension. An estimation of the fine sediment deposition rate and a discussion on the sediment dynamics is proposed from these measurements.

36th IAHR world congress, La Haye, NLD, 28-/06/2015 - 03/07/2015; International audience; Alpine gravel-bed rivers are characterized by very poorly sorted sediments and significant grain sorting is generally observed on gravel bars. The grain size variability may significantly influence the inception of movement for each of the classes represented over a gravel bar. The purpose of this paper is to present some field measurements achieved on the Arc en Maurienne River, France. The main objective is to characterize the dynamics of fine and coarse sediments for conditions close to the incipient motion of gravels and for different degrees of clogging of the river bed. The field campaign was carried out on a gravel bar located 10 km downstream of St Jean de Maurienne during the dam flushing event on June 17th, 2014. Six patches including tagged pebbles (using PIT-tag) were built up with three different characteristics: clean patches formed with gravels and pebbles only, patches with a natural mixture where tagged pebbles were substituted to naturally arranged ones, and patches artificially clogged with fine sediments. These patches were located on the side of a secondary channel on the gravel bar. Surface grain size analyses of the gravel (using the Woolman method and photo analyses using BaseGrain) as well as topographic measurements were achieved the day before the event. During the flushing event, surface velocities over the gravel bar were measured thanks to video analysis (LSPIV). Water levels and mean slope in the secondary channel were measured thanks to pressure gauges positioned on the side of the secondary channel. An estimation of the bed shear stresses over the patches was thus possible all along the event. Intense water sampling was also carried out both upstream and downstream the secondary channel. During the postevent survey the day after, the PIT-tag search showed that the coarse particles did not move. On the other hand, a significant amount of fine sediments were deposited on the patches and infiltrated on the clean patches. Grain size analysis showed that deposited sediments were much coarser than sediments in suspension. An estimation of the fine sediment deposition rate and a discussion on the sediment dynamics is proposed from these measurements.

L'objectif de cette expérience de terrain est de mieux comprendre la dynamique sédimentaire in situ dans le cas d'une rivière alpine avec une granulométrie très étendue (l'Arc en Maurienne) et pour des conditions proches de la mise en mouvement des galets. En particulier, nous cherchons à mieux comprendre la dynamique d'infiltration et de dépôt des matériaux fins (limons, sables) et l'impact du degré de colmatage de la matrice grossière sur le début de mise en mouvement des galets. Ce document décrit les moyens mis en oeuvre, les méthodologies utilisées, ainsi que les résultats de l'expérience réalisée au cours de la chasse de l'Arc du 9 juin 2015. Il reprend ainsi partiellement de premiers travaux réalisés lors de la chasse du 17 juin 2014 (Camenen et al., 2015a et b).

International audience; Several formal mistakes can be found in the research paper published by Le Coz et al. [2012] in Flow Measurement and Instrumentation. Their conclusions on the introduced method are still valid but the following errors may be detrimental to its correct implementation by others.; Plusieurs erreurs formelles peuvent être trouvées dans l'article scientifique publié par Le Coz et al. [2012] dans Flow Measurement and Instrumentation. Leurs conclusions sur la méthode introduite sont toujours valables mais les erreurs suivantes peuvent nuire à sa bonne mise en ½oeuvre par d'autres.

International audience; The objective of this article is to investigate the major issues associated with the calibration of the pollutant dispersion in 1-D hydraulic models applied to river networks, especially large, complex, artificializedones where ecological and socio-economical threats are important. Such issues are illustrated and discussedusing the results of five fluorescent tracer experiments conducted in contrasted open-channel systems,ranging from a simple trapezoidal canal to a more complex river network. Experimental dispersion values were quantified using both the change of moment method and a simple fit-by-eye procedure for eight river reaches with homogeneous hydraulic conditions and an achieved tracer mixing and dispersive equilibrium. Since dispersion coefficient values depend on the assumed dispersion model, ideally they should be calibrated using the same model in which they are to be used, as was done in this study. Wealso derived concurrent longitudinal dispersion values using the velocity field measured by hydro-acoustic profilers (ADCP), which appears as a promising and cost-efficient technique for documenting dispersion in large river systems. It appears that the formulae for which the fit was mainly based on the cross-sectional aspect ratio are generally more appropriate for field data than those which are sensitive to the velocity to shear velocity ratio. The interpretation of complex dispersion and mixing processes, along with the selection of relevant dispersion coefficient predictors are key to minimizing errors in the numerical simulation of pollution dynamics in river networks.

In the context of flash floods, or in ungauged basin, we propose to use the acquired video and posted online by witnesses. The preliminary work carried out since 2012 on this issue were used to develop and validate an image sequence processing methodology to overcome the difficulties related to the amateur nature of video capture : camera movements , known optical sensor . This methodology is now stabilized and requires free software tools freely available , including Fudaa - LSPIV ( Irstea / EDF ) . This procedure explain the processing of witness films for the analysis of velocities and flow rates.; Dans le contexte de crues rapides, ou dans des bassins non instrumentés, ou bien encore d’inondations urbaines sans jaugeages, nous proposons d’utiliser des vidéos acquises puis mises en ligne par des témoins. Les travaux préalables menés depuis 2012 sur ce sujet ont permis de développer et valider une méthodologie de traitement des séquences d’images pour pallier les difficultés liées au caractère amateur de l’acquisition vidéo : mouvements de la caméra, optique inconnue du capteur. Cette méthodologie est maintenant stabilisée et ne requiert que des outils logiciels gratuits et disponibles librement, dont Fudaa-LSPIV (Irstea/EDF). Afin de rendre son application possible par d'autres utilisateurs, voilà un mode opératoire pour le traitement des films amateur en vue de l'analyse des vitesses et débits.

International audience; This paper presents a coupled observation and modelling strategy aiming at improving the understanding of processes triggering flash floods. This strategy is illustrated for the Mediterranean area using two French catchments (Gard and Ardèche) larger than 2000 km2. The approach is based on the monitoring of nested spatial scales: (1) the hillslope scale, where processes influencing the runoff generation and its concentration can be tackled; (2) the small to medium catchment scale (1–100 km2), where the impact of the network structure and of the spatial variability of rainfall, landscape and initial soil moisture can be quantified; (3) the larger scale (100–1000 km2), where the river routing and flooding processes become important. These observations are part of the HyMeX (HYdrological cycle in the Mediterranean EXperiment) enhanced observation period (EOP), which will last 4 years (2012–2015). In terms of hydrological modelling, the objective is to set up regional-scale models, while addressing small and generally ungauged catchments, which represent the scale of interest for flood risk assessment. Topdown and bottom-up approaches are combined and the models are used as “hypothesis testing” tools by coupling model development with data analyses in order to incrementally evaluate the validity of model hypotheses. The paper first presents the rationale behind the experimental set-up and the instrumentation itself. Second, we discuss the associated modelling strategy. Results illustrate the potential of the approach in advancing our understanding of flash flood processes on various scales.

International audience

International audience; The non‑contact surface velocity measurement using SVR (Surface Velocity Radar) can be used to measureriver discharge during floods. This method convinces hydrometry services because it is quick and simple to apply.The SVR is a complimentary instrument to add to the field panoply, especially for flood measurements. For computingdischarge from surface velocities, additional measurements (bathymetry, velocity profiles, water level) are needed, and avelocity coefficient has to be estimated for each site. Mean velocity and surface velocity are linked through this coefficient. This study explains the field procedure suggested by Irstea (National Research Institute of Science and Technology for Environment and Agriculture) for gauging streams with a SVR system, with a two‑way procedure to improve the discharge measurement accuracy during fast flood with fast water level variations. Some application results are presented in different rivers, with a comparison between the radar method and other conventional discharge measurements. The quality of the results is very encouraging.; La technique de mesure des vitesses de surface par radar mobile séduit les équipes d'hydrométrie du fait desa rapidité et de la simplicité de sa mise en oeuvre pour des jaugeages en crue. Les radars mobiles viennent ainsi compléter la flotte d'instruments déjà disponible dans les équipes. L'intérêt de ces radars et de cette technique est de pouvoir explorer le champ de vitesse de surface sans contact avec la rivière. Le calcul du débit à partir de ces mesures partielles nécessite des mesures complémentaires, notamment de bathymétrie et de hauteur d'eau. L'évaluation du coefficient de vitesse est aussi un point important. Cette technique est particulièrement bien adaptée aux mesures en crue. Cette étude présente le protocole de mesure proposé par Irstea pour le jaugeage par radar mobile, qui propose notamment une solution de déploiement pour les cas où la hauteur d'eau varie très rapidement dans le cours d'eau. Des cas d'application sur des sites variés sont présentés notamment lorsque la technique par radar a été testée et comparée avec d'autres méthodes. Les résultats sont très encourageants.

International audience; Les observatoires de long terme en environnement permettent d'acquérir une grande quantité de données. Se posent alors les questions de leur bancarisation, leur gestion par les équipes productrices, et leur mise à disposition sur Internet. Le projet BDOH (base de données pour les observatoires en hydrologie) vise à développer pour cela un outil performant, pour les données issues des observatoires hydrologiques d'Irstea. BDOH permet notamment: la visualisation graphique et le téléchargement en temps réel des chroniques, l'import et export de données sous forme de fichiers texte à différents formats avec possibilité d'interpolation du pas de temps, le calcul automatique de données indirectes via des lois de transformation de type courbes de tarage, la gestion de plusieurs niveaux d'utilisateurs avec des accès et droits différenciés, une interface cartographique conviviale.Le projet implique 4 équipes / unités de recherche d'Irstea associées au pôle Informatique Scientifique de la Direction des systèmes d'information, qui assure le développement informatique. Une pré-version est actuellement en cours de test.

Dans le cadre de l’Action 8, l’OSR a réalisé un suivi sédimentaire de la chasse du Haut-Rhône complémentaire des suivis réglementaires assurés par la CNR et le Grand Lyon. Les suivis décrits dans ce rapport ont eu pour objectif de quantifier et d'étudier la variabilité spatio-temporelle des flux de matières en suspension (MES) et de certains contaminants et paramètres d'intérêt associés, générés dans le Haut-Rhône par l'abaissement de la retenue de Génissiat (semaine 1) et par la chasse de la retenue de Verbois (semaine 2). Les opérations de chasse ont participé en deux semaines à la station de Jons à près de 30% du flux annuel de MES et près de 25% du flux annuel en polychlorobiphényles et mercure. Les flux de MES engendrés par les reprises de dépôts au cours des crues suivantes ont également été suivis dans le cadre de la surveillance des stations pérennes et du groupe d'intervention en crues.

International audience; During violent floods, the use of intrusive instruments is often dangerous or impossible. Only remote measurements or observations of the flow from bridges or banks are possible.

Une nouvelle méthode de calcul de l'incertitude des débits mesurés par exploration du champ des vitesses a été développée et testée avec succès sur une série d'exemples d'application. Cette méthode a été construite comme une généralisation de la méthode conventionnelle de la norme ISO748 pour pallier les inconvénients identifiés de cette dernière méthode. En particulier, des méthodes de calcul direct pour les composantes d'incertitude liées à l'intégration spatiale ont été proposées au lieu des valeurs informatives tabulées dans la norme ISO 748. Les extrapolations de débit sur les bords et dans les couches de surface et de fond sont explicitement prises en compte, ainsi que la distribution des verticales à travers la section transversale. La nouvelle méthode semble être plus polyvalente mais aussi simple et robuste que la méthode ISO 748. Elle peut être facilement mise en oeuvre dans les logiciels habituels de dépouillement des jaugeages.

Comparaison de méthodes de mesure du débit des petits cours d'eau. Journées d'intercomparaison des 17 et 18 mai 2011. Présentation et analyse des résultats.

Ce rapport présente les sites de mesure sur le bassin versant de l'Arc et son affluent l'Arvan. Une description technique des outils de mesure y est faite ainsi que la présentation des données collectées et le recensement des incidents d'exploitation.